1. Field of the Invention
The present invention relates to a catalyst composition for polymerizing alpha-olefins, a method for producing such a catalyst and to a method of polymerizing alpha-olefins with such a catalyst. More particularly, the invention relates to a high activity catalyst composition which produces high density, high molecular weight alpha-olefin polymers, having a relatively broad molecular weight distribution, and to the polymerization process utilizing such a catalyst composition.
2. Description of the Prior Art
Linear low density polyethylene polymers possess properties which distinguish them from other polyethylene polymers, such as ethylene homopolymers. Certain of these properties are described by Anderson et al, U.S. Pat. No. 4,076,698. Such polymers are usually prepared from alpha-olefins in the presence of catalysts commonly referred to as Ziegler or Ziegler-Natta catalysts. Such catalysts usually contain various combinations of a magnesium compound, a compound of a transition metal, e.g., titanium or vanadium, and a co-catalyst, e.g., an aluminum alkyl.
Graff, U.S. Pat. No. 4,173,547, Stevens et al, U.S. Pat. No. 3,787,384, Strobel et al, U.S. Pat. No. 4,148,754, and Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, each describe various polymerization processes suitable for producing forms of polyethylene other than linear low density polyethylene, per se.
Stevens et al, U.S. Pat. No. 3,787,384, and Strobel et al, U.S. Pat. No. 4,148,754, describe catalysts prepared by first reacting a support (e.g., silica containing reactive hydroxyl groups) with an organomagnesium compound (e.g., a Grignard reagent) and then combining this reacted support with a tetravalent titanium compound.
Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, describe a catalyst which is the reaction product of an organomagnesium compound (e.g., an alkylmagnesium halide) with a tetravalent titanium compound. The reaction of the organomagnesium compound with the tetravalent titanium compound takes place in the absence of a support material.
A vanadium-containing catalyst, used in conjunction with triisobutylaluminum as a co-catalyst, is disclosed by W. L. Carrick et al in Journal of American Chemical Society, Volume 82, page 1502 (1960) and Volume 83, page 2654 (1961).
Altemore et al, U.S. Pat. No. 3,899,477, disclose a catalyst comprising a titanium halide, a vanadium halide and an organoaluminum compound. The catalyst is admixed with a mixture of an alkylaluminum sesquiethoxide and a trialkylaluminum prior to the use thereof in the polymerization of ethylene to produce high molecular weight and broad molecular weight distribution polymers. The catalyst may be supported on a support by preparing a solution or a slurry thereof and admixing it thoroughly with the support.
Ort et al, U.S. Pat. No. 3,956,255, disclose a supported catalyst composition made by depositing on a previously-treated silica gel a compound of vanadium, a trialkylaluminum, and an alkylaluminum alkoxide. The silica must be treated with an alkylaluminum, an alkylaluminum alkoxide or mixtures thereof, since the catalyst made with untreated silica has low activity.
Best, U.S. Pat. No. 4,607,019, discloses an olefin polymerization catalyst composition producing high molecular weight and broad molecular weight distribution polyolefins comprising a vanadium-containing catalyst component and an aluminum alkyl co-catalyst. The vanadium-containing catalyst component is prepared by contacting an inert support with an organoaluminum compound, a halogenating agent and a vanadium compound.
Best, U.S. Pat. Nos. 4,579,835 and 4,634,751, disclose vanadium-based olefin polymerization catalyst compositions comprising a support material, treated with an organoaluminum compound, an acyl halide and a vanadium compound, activated with an aluminum alkyl cocatalyst.
Best, U.S. Pat. Nos. 4,578,374 and 4,579,834, disclose vanadium- and magnesium-containing supported olefin polymerization catalyst compositions.
With some of the catalysts described above, high yields of good quality, high-molecular weight, solid polymers of ethylene and other olefins may be produced. Generally, these are linear polymers of high density, i.e., 0.930 g/cc and above, with the molecular weight of the polymers falling within a wide range from 2,000 to 300,000 and even as high as 3,000,000 or more. The density and molecular weight characteristics of these polymers render them satisfactory for many uses and they have, in fact, in recent years found extensive commercial use in a variety of applications. However, the polymer products obtained are not always suitable for specialty uses because they do not have the desired molecular weight distribution. Generally, high density and high molecular weight polymers are preferred for their superior strength characteristics. However, such polymers tend to have narrow molecular weight distribution which renders them difficult and expensive to process. Conversely, high density polymers having comparatively broad molecular weight distribution are more easily processed but they do not have satisfactory strength properties. A polymer having balanced molecular weight and molecular weight distribution properties would therefore be desirable for use over a wide range of applications.